Hans A. Bethe, a German-born physicist, recognizes that the fusion of hydrogen nuclei to form deuterium releases energy. He suggests that much of the energy output of the Sun and other stars results from energy-releasing fusion reactions in which four hydrogen nuclei unite and form one helium nucleus.

Frederic Joliotdemonstrates the possibility of splitting the atom of uranium isotope 235.

Albert Einsteinís
first letter to PresidentFranklin Roosevelt leads to the formation of the Committee on Uranium. The letter, originally drafted by Leo Szilard, states, "that the element uranium may be turned into a new and important source of energy in the immediate future. Certain aspects of the situation which has arisen seem to call for watchfulness and, if necessary, quick action on the part of the Administration." After the bombing of Hiroshima, Einstein states, "I could burn my fingers that I wrote that first letter to Roosevelt."